The boiler represented by the diagram beneath, consists of a series of tubes of cast iron, connected by screw-bolts with the under side of a larger vessel, or magazine of the same material. This is furnished with four, and in some cases with five apertures; the first of which, A, is intended for the admission of water, to supply the waste which continually arises from evaporation, which is effected by means of a small forcing-pump, as it will be evident that the column must be carried to a considerable height, before its weight can so far overcome the resistance of the steam within the tube, to allow of its entering by the ordinary method.

Mr. Woolf usually employs two safety-valves which are placed at B, while C represents the man-hole, and D the pipe by which the steam is conveyed to the engine.*

In Mr. Woolf's specification, a method is pointed out for applying this plan to the boilers of steam engines already in use, by placing a series of cylinders beneath the present boilers, and connecting them with each other, and with the boiler above. The tubes may be made of any kind of metal, but cast iron is the most convenient; their size may also be varied, but in every case care should be taken not to make the diameter too large; for it must be remembered, that the larger the diameter of any single tube is in such a boiler, the stronger it must be made in proportion, to enable it to bear the same expansive force of steam as the smaller cylinders. It is not essential, however, to the invention, that the tubes should be of different sizes; but the upper cylinders, and more especially the one which is called the steamcylinder, should be larger than the lower ones, it being the reservoir, as it were, into which the lower ones empty themselves.

bolts and nuts; a sheet of woollen or linen cloth coated with cement, being first introduced to unite the intervening surfaces. The cement best adapted for this purpose, from its durability and power of withstanding the action of steam, may be thus prepared :-Take two ounces of sal ammoniac, one ounce of flour of sulphur, and sixteen ounces of cast-iron filings; these, after being well mixed in a mortar, must be placed in a dry situation, and when wanted for use one part of the above mixture must be blended with twenty parts of clean filings, and saturated with a little water. On being applied to the joint it will shortly be. come as hard as the metallic surface on which it is placed,

The following general directions are given respecting the quantity of water to be kept in a boiler of this construction; viz. it ought always to fill, not only the whole of the lower tubes, but also the great steam-cylinder, A, to about half its diameter, that is, as high as the fire is allowed to reach. And in no case should it be allowed to get so low as not to keep the vertical necks, or branches which join the smaller cylinders to the great cylinder, full of water, for the fire is only beneficially employed when applied, through the medium of the interposed metal, to water, to convert it into steam; and indeed, the purpose of the boiler would in some measure be defeated, if any of the parts of the tubes thus exposed to the direct action of the fire, should present a surface of steam instead of water, to receive the transmitted heat; this, however, must, more or less, be the case whenever the lower tubes, and even a part of the upper, are not kept filled with the water.

Respecting the furnace for this kind of boiler, it should always be so built as to give a long and waving course to the flame and heated air, so that they may, in the most effectual manner, strike against the sides of the tubes which compose the boiler, and so give out the greatest possible portion of their heat before they reach. the chimney: unless this be attended to, there

will be a much greater waste of fuel than necessary, and the heat communicated to the contents of the boiler will be less from a given quantity of fuel.

Mr. Maudslay, in his Portable Engine, dispenses with the beam usually employed for connecting the fly-wheel crank with the piston-rod ; and, in this respect, as well as in the working of the valves, his engine materially differs from those we have already described.

Plate V. Fig. 1. Front elevation of a ten-horse power engine.

Fig. 2. Longitudinal section of ditto, on the centre line.

Fig. 3. End view of ditto.

A. Cast-iron frame of the engine.

B. The cylinder.

C. The piston, furnished with a rod D, and a cross head and socket E.

F. Guide wheels, which keep the piston and rod in a vertical position.

G. Frame for ditto, in which the wheels FF are made to work.

H. Side rods, which serve to connect the cross head E with the double crank II.

II. Two cranks, made to turn in the plummer. block, or bearing, JJ, at each side of the frame, and to which the fly-wheel shaft K is connected by a coupling-box or clutch, at the end next the engine.

K. Fly-wheel shaft, working in a plummer-block on the wall.

L. Coupling-box, connecting the engine with the fly-wheel shaft.

M. The fly-wheel.

NN. Two excentric wheels, supported by the crank-shaft K, the action of which give motion to the two beams O and T, by means of the connecting-rods PP.

O. The beam which works the cold-water pump S.

PP. Two connecting-rods.

Q. The double bearing, on which the coldwater pump-beam works.

R. A rod which serves to connect the bucket of the cold-water pump with the beam O.

S. The barrel of the cold-water pump.

T. Beam which works the air and hot-water pumps, and to which motion is communicated by the connecting-rods P, as before described.

U. The slings which connect the air-pump rod to the end of the beam T.

V. The double bearing, or centre, on which the air-pump beam T works.

W. The air-pump bucket.

X. Air-pump cylinder.

Y. Hot-water pump, worked by a small rod, attached to the air-pump beam.

Z. Feed-pipe, to supply the boiler with hot

water.